1. Field of the Invention
The present invention relates to a modified magnetron high-frequency discharge plasma generating apparatus and to a semiconductor manufacturing method, and more particularly to an apparatus for performing various processes on rectangular substrates using a plasma, such as plasma dry etching of a film formed on the surface of a large-area rectangular substrate, or suitable as a plasma CVD (chemical vapor deposition) apparatus for producing a thin film on the surface of a substrate using a plasma-induced vapor phase reaction.
2. Description of the Related Art
In production processes for solid state devices such as semiconductor devices, it is necessary to subject substrates to predetermined processes. One such substrate processing method involves introducing a reactive gas into the reaction chamber in which the process will be performed, and applying heat to induce the gas to react so as to deposit a film on the substrate surface. This method requires relatively high temperatures, which may have a number of adverse effects on devices. Thus, more recently, plasma CVD techniques in which the energy needed to activate the reaction is supplied by a plasma generated through a glow discharge have come into use.
Plasma CVD techniques are also employed for film deposition on rectangular substrates for use in liquid crystal displays of various types, solar cells, and the like. In plasma CVDxe2x80x94the plasma process used for typical large-area rectangular substratesxe2x80x94uniform high-density plasma is needed to accommodate larger-area substrates and to improve apparatus through-put. Plasma sources to meet this need are currently under development. As used herein, xe2x80x9ctypical large-area rectangular substratesxe2x80x9d@refers to those of 860 mmxc3x97650 mm class or larger.
However, the plasma sources most relied upon currently are ordinary parallel plate high-frequency discharge plasma sources. Since ordinary parallel plate high-frequency discharge plasma sources generate plasma rather inefficiently, the low film deposition rate poses problems when depositing a film on a substrate surface using plasma CVD. Also, the uniformity of film thickness cannot be said to be adequate at present.
To accommodate rectangular substrates, ordinary parallel plate high-frequency discharge plasma sources currently in use are designed with rectangular electrodes, but since the electric field tends to become concentrated at the corners of the electrodes, plasma density tends to be higher at the electrode corners, with the rate of film deposition being higher in proximity to the electrode corners as well. Using an ordinary parallel plate high-frequency discharge plasma source, when it is attempted to increase the high-frequency power input in order to increase the throughput of the apparatus, high sheath voltage tends to form on the cathode electrode surface to which the high frequency is applied, resulting in a serious problem of metal contamination from the electrode surface. As used herein, xe2x80x9csheath voltagexe2x80x9d@refers the potential of the substrate surface relative to the average potential of the plasma space.
Besides the parallel plate high-frequency discharge plasma sources, electron-cyclotron resonance (ECR) plasma sources, inductively-coupled plasma (ICP), micro surface wave, helicon wave, and other high-density plasma sources are also available, but while these give adequate plasma densities, they still have not reached plasma uniformity levels adequate for processing of large-area substrates.
On the other hand, a modified magnetron plasma source employing annular high-frequency electrodes has been disclosed (JP(A) 7-201831). The plasma generating apparatus disclosed in this publication generates plasma by producing a magnetron discharge from a high-frequency electrical field generated by a cylindrical discharge electrode and magnetic fields generated by annular permanent magnets.
The plasma generating apparatus disclosed in the above publication, however, has the drawback that high density plasma cannot be generated in the diametral central area of the plasma generation zone. This is due to the fact that plasma is generated predominantly on the surface of the discharge electrode. Accordingly, any plasma surface processing apparatus designed using this plasma generating apparatus will not be capable of surface processing under conditions of uniform plasma density. This problem can be solved by locating the susceptor some distance from the discharge electrode in the axial direction thereof.
This design, however, while affording surface processing under conditions of uniform plasma density, produces a new problem, namely, inability to perform surface processing under conditions of high plasma density, owing to the excessively large volume of the vacuum chamber. In a plasma generating apparatus of this kind, plasma density declines further away from the discharge electrode in the axial direction thereof due to plasma diffusion loss. Thus, with this design the rate of surface processing tends to be slow, and the efficiency of utilization of the gas and the efficiency of utilization of the electrodes tend to be poor.
Accordingly, there is a need for an apparatus capable of generating high density plasma in both the central area of the discharge electrode as well as in the peripheral area.
With the foregoing in view, it is an object of the present invention to provide a modified magnetron high-frequency discharge plasma generating apparatus and a semiconductor manufacturing method that solve the problems pertaining to the conventional art so as to allow plasma processing of large-area rectangular substrates to be conducted at high speed.
The plasma generating apparatus recited in claim 1 comprises: a vacuum chamber of rectangular cross section having a plasma generating zone provided therein; gas introducer for introducing a discharge gas into this vacuum chamber; an exhaust for exhausting the atmosphere within said vacuum chamber; a fistulous discharge electrode of rectangular shape (hereinbelow termed simply xe2x80x9crectangular fistulousxe2x80x9d), arranged surrounding said plasma generating zone, for inducing discharge of the gas introduced into said plasma generating zone by said gas introducer; first high-frequency power supplier for supplying high-frequency power to said discharge electrode for inducing discharge of said gas; magnetic lines of force generator for producing magnetic lines of force within said plasma generating zone; and a pair of rectangular parallel plate electrodes, arranged so as to sandwich said plasma generating zone in the direction of the central axis of said discharge electrode and to define a range of said plasma generating zone in the direction of this central axis. xe2x80x9cRectangular fistulousxe2x80x9d refers to a fistulous configuration having a rectangular aperture.
The gas introducer has the function of introducing the discharge gas and the reactive gas needed for plasma processing into the vacuum chamber. The exhaust has the function of exhausting the atmosphere present within the vacuum chamber to the outside, Since the vacuum chamber for processing the substrate is of rectangular configuration like the substrate, the vacuum chamber need not have excessively large volume in order to process a large-area rectangular substrate, thus improving the efficiency of utilization of the gas and the efficiency of utilization of the high-frequency discharge electrode. Since the discharge electrode for generating the plasma is also rectangular, the space in which the plasma is generated has the same rectangular shape as the substrate. Accordingly, the installation area required for the vacuum chamber can be reduced further, as a result reducing the area occupied thereby in the clean room in which it is installed and reducing the costs associated with clean room maintenance. Interaction between the high-frequency electrical field generated by supplying high-frequency power to the discharge electrode and the magnetic field created by the magnetic lines of force produced by the magnetic lines of force generator affords efficient gas discharge so that a high-density plasma may be formed within the plasma generating zone. With this arrangement, the efficiency of plasma generation may be improved by, for example, 10 times or more relative to ordinary capacitively coupled parallel plate systems.
According to the plasma generating apparatus recited in claim 2, the magnetic lines of force generator produces magnetic lines of force comprising portions that extend approximately parallel to the central axis of said fistulous discharge electrode of rectangular shape, these parallel portions increasing in length closer to said central axis. By producing magnetic field components that extend parallel to the rectangular fistulous discharge electrode surface, a magnetron discharge is created at the electrode surface through interaction of the electrical field and the magnetic field when high-frequency power is applied to the electrode, whereby a plasma may be generated efficiently even at low gas pressure. Additionally, by producing magnetic field components that extend parallel to the rectangular fistulous discharge electrode surface, electronsxe2x80x94which have low massxe2x80x94are trapped in the magnetic field and thus do not readily impinge on the electrode surface, whereas heavier-mass ions are allowed to impinge on the electrode surface unaffected by the magnetic field, so that fewer charges build up on the electrode surface, sheath voltage on the electrode surface is minimal, and metal contamination from the electrode surface is reduced.
According to the plasma generating apparatus recited in claim 3 or 4, said magnetic lines of force generator comprises permanent magnets arranged coaxially with said rectangular fistulous discharge electrode so as to surround said discharge electrode, said two permanent magnets being arranged along the central axis, having polarities radially magnetized in opposite directions to each other. The use of permanent magnets of rectangular configuration (hereinbelow termed simply xe2x80x9crectangular permanent magnetsxe2x80x9d) to generate a magnetic field affords ample magnetic field strength in proximity to the rectangular fistulous discharge electrode surface, whereas distance-wise the magnetic field strength attenuates sharply a predetermined distance, for example about 2 cm, away from the electrode surface, so that the effects thereof on the substrate can essentially be ignored. By manipulating the distance of the two permanent magnets it is possible to control magnetic field strength at the rectangular fistulous discharge electrode surface.
According to the plasma generating apparatus recited in claim 5 or 6, the magnetic lines of force on the rectangular fistulous discharge electrode surface are such that the flux density of the component coextensive with the central axis of the discharge electrode is lower proceeding from the center of said discharge electrode surface towards the ends of the central axis, and the directional component orthogonal to a central axis is higher proceeding from the center of said discharge electrode surface towards the ends of the central axis. Such a magnetic field distribution is readily achieved using the plasma generating apparatus recited in claim 3. By generating the aforementioned magnetic field distribution using two permanent magnets, it becomes possible to trap high-energy electrons on the rectangular fistulous discharge electrode surface, so that the energy of the electrons can be utilized efficiently to ionize neutral gas molecules.
In the above mentioned plasma generating apparatus, it is preferable to comprises second high-frequency power supplier for supplying high-frequency power to one of a pair of rectangular parallel plate electrodes, whereby the high-energy electrons trapped by the magnetic lines of force produced by the magnetic lines of force generator are caused to move in reciprocating fashion in a direction approximately parallel to the central axis of said rectangular fistulous discharge electrode; and controller for controlling the ratio of high-frequency powers supplied by the first and second high-frequency power suppliers to the discharge electrode and to one of said rectangular parallel plate electrodes, respectively.
Through interaction of the magnetic lines of force recited in claim 5 or 6 and the high-frequency electrical field applied across the parallel plate electrodes by the second high-frequency power supplier, plasma may be generated efficiently in the central zone in the vacuum chamber. This is because the magnetic lines of force extending perpendicular to the parallel plate electrodes are longer in the central portion and shorter in the outlying portions. The plasma generated by the high-frequency power applied to the rectangular fistulous discharge electrode by the first high-frequency power supplier is generated mainly in proximity to the rectangular fistulous discharge electrode. For this reason, plasma density distribution can be controlled through control of the ratio of the energy supplied by the first and second high-frequency power supplier.
In the plasma generating apparatus, it is preferable to comprises a system for controlling the phase of the high-frequency power supplied by the first and second high-frequency power supplier. By controlling the phase of the first and second high-frequency power, the space potential of the plasma can be controlled so as control the energy of the charged particles flowing into the substrate. Controlling plasma space potential also makes is possible to reduce plasma damage to the electrode surfaces.
Further, in the plasma generating apparatus, it is preferable that the other of the pair of rectangular parallel plate electrodes is connected to a base potential.
Here, the second high-frequency power may be applied to the top parallel plate electrode, i.e., the one opposite the substrate holder (susceptor), with the bottom parallel plate electrode (on which the substrate rests) being electrically grounded. Since the second high-frequency power is applied not to the electrode on which the substrate rests but rather to the opposite electrode, charge buildup on the substrate surface is negligible. The energy of the charged particles flowing into the substrate is quite low. This invention is effective as a process that does not require sheath voltage on the substrate surface. Alternatively, the second high-frequency power can be applied to the bottom parallel plate electrode, i.e., the susceptor, with the top parallel plate electrode being electrically grounded. By applying the second high-frequency power to the susceptor it is possible to produce a high sheath voltage on the substrate surface and to accelerate the charged particles flowing into the substrate.
Further, in the plasma generating apparatus, the other of the pair of parallel plate electrodes may be electrically floated.
Here, the second high-frequency power may be applied to the bottom parallel plate electrode, i.e., the susceptor, with the top parallel plate electrode being electrically floated. With the top parallel plate electrode electrically floated, not only is the sheath voltage forming on the top parallel plate electrode surface lower than with the apparatus of claim 7, but the plasma space potential is also lower, thus reducing plasma damage to the top parallel plate electrode and the reaction chamber wall. Alternatively, the second high-frequency power may be applied to the top parallel plate electrode, i.e., that opposite the susceptor, with the bottom parallel plate electrode being electrically floated. With the susceptor electrically floated, the energy of the charged particles flowing into the substrate can be better controlled than with the apparatus which the other of the pair of rectangular parallel plate electrodes is connected to the base potential. Also, electrically floating the susceptor results in low space potential in the plasma, thus minimizing plasma damage to the electrode surfaces and reaction chamber wall.
Further, in the plasma generating apparatus, it is preferable that the other of the pair of rectangular parallel plate electrodes is used as a holder for holding the substrate when a predetermined processes is performed on the substrate using a plasma. Where the plasma generating apparatus is used for plasma surface treatments, this other parallel plate electrode can be used as a holder for holding the substrate, thus simplifying the design.
Further, in the plasma generating apparatus, it is preferable that the rectangular fistulous discharge electrode constitutes a portion of the wall of said vacuum chamber, with a dielectric material (e.g., ceramic, quartz glass, etc.) being interposed at the joint between the vacuum chamber and the discharge electrode. The dielectric material interposed in the joint serves to maintain the vacuum seal. The resulting reaction chamber has a simple internal construction and is effective against particles. By adopting the design of the invention, it is furthermore possible to situate the permanent magnets in proximity to the inside surface of the rectangular fistulous discharge electrode so that an effective magnetic field may be formed on the discharge electrode surface. Additionally, since the exterior of the rectangular fistulous discharge electrode to which high-frequency power is applied is in contact with the air, temperature control of the discharge electrode is a simple matter.
According to the plasma generating apparatus recited in claim 7 or 8, the rectangular fistulous discharge electrode is situated within the vacuum chamber, with the gap between the rectangular fistulous discharge electrode and the inside wall of said vacuum chamber being less than half of the mean free path of electrons in the plasma under the gas pressure that will be employed in the process. This design simplifies the construction of the vacuum chamber. The purpose of making the gap in between the rectangular discharge electrode and the vacuum chamber smaller than half of the mean free path of electrons in the plasma is to prevent discharge from occurring within the gap.
According to the plasma generating apparatus recited in claim 9 or 10, the rectangular fistulous discharge electrode is situated within the vacuum chamber, with a dielectric material (e.g., high purity aluminum nitride, quartz glass, ceramic, etc.) being interposed in the gap between the rectangular fistulous discharge electrode and the inside wall of the vacuum chamber. The length of the dielectric material in the axial direction thereof is greater than the length of the rectangular fistulous discharge electrode in the axial direction thereof. This prevents discharge from becoming concentrated at the edges of the rectangular fistulous discharge electrode. By adopting the design of the invention, it is possible to fabricate the vacuum chamber in sections, thereby reducing production costs for vacuum chambers intended for use with large-area substrates.
In the plasma generating apparatus. It is preferable to comprises a gas shower plate for blowing out an even flow of a gas (a process gas, for example) onto the parallel plate electrode opposite the susceptor, in order to bring about more uniform processing of the surface of a rectangular substrate. The gas shower plate is of rectangular configuration like the substrate, and is provided with gas diffusion holes at equal intervals for producing uniform process gas coverage over the entire face of the substrate. To prevent abnormal discharge at the gas diffusion holes, jet hole diameter is 1 mm or smaller, and preferably 0.6 mm or smaller. By jetting the process gas by means of a gas shower plate arrangement it is possible to readily achieve uniform plasma processing of a substrate surface. Also, the need for positioning, as is required with process gas supplied via a nozzle arrangement, is obviated, giving the apparatus better operation and reproducibility.
According to the plasma generating apparatus recited in 11 or 12, at least two rectangular permanent magnets are symmetrically nested on one of the pair of rectangular parallel plate electrodes. By arranging the permanent magnets on one of the parallel plate electrodes (the top electrode, for example) provided with a gas shower plate, it becomes possible to create magnetron discharge at the plasma generating zone face of the top electrode through the interaction of magnetic field produced by the permanent magnets and the high-frequency electrical field applied to the electrode. This in turn makes it possible to generate a plasma efficiently at low pressure, allowing the process to be conducted efficiently. In preferred practice, the number of permanent magnets arranged on the top electrode will be an even number, in order to weaken magnetic field strength at the substrate surface. An odd number will produce a divergent magnetic field, as a result of which magnetic field strength will not be attenuated at the substrate surface. Where the magnetic field at the substrate surface is too strong to be ignored (20 gauss or above, for example), an uneven plasma distribution will be produced at the substrate surface, making uniform processing impossible. The magnetic field also causes charges to build up on the substrate surface, which may damage the substrate.
According to the plasma generating apparatus recited in claim 13 or 14, said rectangular fistulous discharge electrode is provided with curvature at the corners thereof. By providing the corners with curvature, it becomes possible to control the rate of plasma generation in the corners.
The semiconductor manufacturing method recited in claim 15 comprises the steps of: providing a vacuum chamber of rectangular cross section having a plasma generating zone provided therein, a fistulous discharge electrode of rectangular shape arranged surrounding said plasma generating zone, and a pair of rectangular parallel plate electrodes arranged so as to sandwich said plasma generating zone in the direction of the central axis of said discharge electrode and to define said plasma generating zone in the direction of this central axis: arranging a substrate within said plasma generating zone; producing a high-frequency electrical field in said plasma generating zone by supplying high-frequency power to said discharge electrode and said parallel plate electrodes; producing a magnetic field in said plasma generating zone; introducing a discharge gas into said plasma generating zone provided within said vacuum chamber while exhausting the atmosphere within said vacuum chamber; producing plasma by inducing discharge of the gas introduced into said plasma generating zone by means of interaction between said high-frequency electrical field and said magnetic field; and and subjecting said substrate to a predetermined plasma process using the plasma so generated.
According to this semiconductor manufacturing method, high-frequency power is supplied to the discharge electrode and the parallel plate electrodes to produce a high-frequency electrical field within the plasma generating zone, and a magnetic field is produced within the plasma generating zone. Discharge gas is introduced into the plasma generating zone while exhausting the atmosphere within the vacuum chamber. Interaction of the high-frequency electrical field and the magnetic field causes the gas introduced into the plasma generating zone to discharge and generate a plasma. The plasma so generated can be used for subjecting a substrate arranged within the plasma generating zone to a predetermined plasma process. Since the vacuum chamber, discharge electrode, and parallel plate electrodes are rectangular, the efficiency of utilization of the gas and the efficiency of utilization of the high-frequency power electrodes when processing a rectangular substrate is improved. Interaction between the high-frequency electrical field generated by supplying high-frequency power to the discharge electrode and the magnetic field created by the magnetic lines of force produced by the magnetic lines of force generator affords efficient gas discharge so that a high-density plasma may be formed within the plasma generating zone. With this arrangement, the efficiency of plasma generation may be improved by, for example, 10 times or more relative to ordinary capacitively coupled parallel plate systems. High quality plasma processing of the substrate is possible as a result. The semiconductor manufactured by the semiconductor manufacturing method is applicable to TFT etc. liquid crystal displays of various types.
In the above mentioned semiconductor manufacturing method, it is preferable that the substrate is subjected to a predetermined plasma process while controlling the ratio of high-frequency powers supplied to said discharge electrode and to said parallel plate electrodes. By manipulating the ratio of high-frequency power supplied to the discharge electrode and the parallel plate electrodes it is possible to control the density distribution of the plasma generated in the plasma generating zone. It is therefore possible to generate a plasma having a uniform density distribution throughout the entire plasma generating zone.
Further, in the above mentioned semiconductor manufacturing method, it is preferable that the substrate is subjected to a predetermined plasma process while setting the internal pressure of said vacuum chamber within the range of from 0.1 Pa to 40 Pa. According to the semiconductor manufacturing method of the present invention, it is possible to produce a magnetron discharge through interaction of an electrical field and a magnetic field, which can be used for efficient plasma generation even at low gas pressures. Thus, high quality plasma processing of substrates is possible even at low pressures of from 0.1 Pa to 40 Pa within the vacuum chamber.